PROJECT SUMMARY In the proposed research, we conduct a randomized-controlled trial with 180 families to test the effectiveness of a parent advocacy training to improve the transition to adulthood for youth with autism spectrum disorder (ASD). The years immediately after high school exit are a critical time period that either makes or breaks a successful transition to adulthood. If they don't go well, disengagement from post-secondary education, work, and social isolation can persist throughout adulthood, leading to significant societal costs. Despite the pressing need to better support youth with ASD during this turbulent time, few interventions for these youth have been developed and even fewer tested. Our preliminary work has demonstrated the efficacy of a 12-week parent training program targeting parents' ability to advocate for services on behalf of their offspring (called the ?Volunteer Advocacy Program-Transition? or VAP-T), in improving the transition to adulthood for youth with ASD. Relative to a wait-list control group, youth whose parents participated in the VAP-T were more likely to be employed or in post-secondary education, and they received more school-based and adult services. The proposed project builds on this pilot work in four important ways: 1) by making modifications to the VAP-T content to make it nationally-applicable and testing whether the VAP-T is effective when delivered across three states; 2) by incorporating the perspective of offspring with ASD into the intervention and data collection; 3) by examining mechanisms by which the VAP-T influences youth outcomes; and 4) by exploring barriers to participation and factors that moderate treatment response. We hypothesize that participating in the VAP-T will improve parents' advocacy ability, leading to higher rates of employment, post-secondary education, social participation, and service access for youth with ASD. We will test this hypothesis by randomly assigning parents of transition-aged youth with ASD (ages 16-26) to either a treatment or active, materials-only control group, and following families over 3 years. We propose four Specific Aims: (1) To use a multi-site randomized- controlled trial to examine whether VAP-T participation increases parent advocacy ability (i.e. the intervention target); (2) To test whether participating in the VAP-T leads to improved youth outcomes (employment, post- secondary education, social participation, service access) during the transition to adulthood; (3) To examine which aspects of parent advocacy ability mediate the relations between VAP-T participation and youth outcomes; and (4) To explore moderators of treatment response and barriers to participation in the intervention. By rigorously testing a new intervention to improve the transition to adulthood for youth with ASD, the proposed research addresses an area of critical need as identified by the 2016-7 Interagency Autism Coordinating Committee Strategic Plan. The project will result in a new intervention to improve outcomes for youth with ASD that can be disseminated through state and local agencies across the nation.